With remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21st century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place.
Lithium secondary batteries are very important to realize such a ubiquitous society. Specifically, lithium secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. In addition, the lithium secondary batteries have also been used as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
As devices, to which the lithium secondary batteries are applicable, are diversified as described above, the lithium secondary batteries have also been diversified such that the lithium secondary batteries can provide outputs and capacities suitable for devices to which the lithium secondary batteries are applied. In addition, there is a strong need to reduce the size and weight of the lithium secondary batteries.
Based on the shape thereof, the lithium secondary batteries may be classified into a cylindrical battery cell, a prismatic battery cell, and a pouch-shaped battery cell. Among these kinds of lithium secondary batteries, much interest is currently focused on the pouch-shaped battery cell, which can be stacked with high integration, has high energy density per unit volume, can be manufactured at low cost, and can be easily modified.
FIGS. 1 and 2 are exploded perspective views typically showing a general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1, a pouch-shaped secondary battery 10 includes a stacked type electrode assembly 20 having pluralities of electrode tabs 21 and 22 protruding therefrom, two electrode leads 30 and 31 respectively connected to the electrode tabs 21 and 22, and a battery case 40, in which the stacked type electrode assembly 20 is received in a sealed state such that the electrode leads 30 and 31 are partially exposed outward from the battery case 40.
The battery case 40 includes a lower case 42 having a depressed receiving part 41, in which the stacked type electrode assembly 20 is located, and an upper case 43 for covering the lower case 42 such that the electrode assembly 20 is sealed in the battery case 40. The upper case 43 and the lower case 42 are connected to each other by thermal welding in a state in which the stacked type electrode assembly 20 is mounted therein to form an upper end sealed part 44, side sealed parts 45 and 46, and a lower end sealed part 47.
As shown in FIG. 1, the upper case 43 and the lower case 42 may be configured as separate members. As shown in FIG. 2, on the other hand, one end of the upper case 43 may be integrally formed at a corresponding end of the lower case 42 such that the upper case 43 and the lower case 42 may be hingedly connected to each other.
In addition, as shown in FIGS. 1 and 2, the pouch-shaped battery cell is configured to have a structure in which electrode terminals constituted by the electrode tabs and the electrode leads connected to the electrode tabs are formed at one end of the electrode assembly. Alternatively, a pouch-shaped battery cell configured to have a structure in which electrode terminals are formed at one end and the other end of an electrode assembly may also be manufactured using the above-described method.
Meanwhile, FIGS. 1 and 2 show the pouch-shaped battery cell having the stacked type electrode assembly. Alternatively, a pouch-shaped battery cell having a wound type or jelly-roll type electrode assembly may also be manufactured using the above-described method.
As shown in FIGS. 1 and 2, the pouch-shaped battery cell is generally configured to have an approximately rectangular hexahedral shape.
However, devices, to which the pouch-shaped battery cell is applied, may be configured to have various shapes other than a rectangular hexahedral shape. The devices may even be configured to have a curved shape. For example, sides of a smart phone may be curved so as to be easier to grip, and a flexible display device may be curved or bent. That is, the flexible display device may be manufactured to have various shapes.
In a case in which a battery cell or a battery pack configured to have a rectangular hexahedral shape is mounted in a device designed so as to have such curved parts or a device that can be curved, however, the efficiency of utilization of the space in the device may be lowered. In recent years, it has been required for the battery cell to be flexible such that the battery cell can be easily mounted in devices configured to have various kinds of designs.
Therefore, there is a high necessity for technology that is capable of securing safety of a battery even when the battery is deformed while solving the above problems.